1. Field of the Invention
The present invention relates to a control apparatus and method for an internal combustion engine for burning an air-fuel mixture with self ignition while auxiliarily using a spark ignition.
2. Description of the Prior Art
Conventionally, as this type of control apparatus for an internal combustion engine, one described, for example, in Laid-open Japanese Patent Application No. 2005-16407 is known. This internal combustion engine is of a type which can be operated by switching between a self ignition combustion mode for burning an air-fuel mixture with compression self ignition while auxiliarily using a spark ignition and a normal combustion mode for burning an air-fuel mixture with flame propagation using a spark ignition. This internal combustion engine comprises an exhaust gas recirculation mechanism, a valve timing varying mechanism, and a valve operation characteristic switching mechanism. This exhaust gas recirculating mechanism recirculates exhaust gases in an exhaust passage to an intake passage as a relatively low-temperature recirculated gas, and comprises an EGR passage, an EGR control valve for controlling a recirculated gas amount, an EGR cooler for cooling down the recirculated gas, and the like.
Also, in the internal combustion engine, a valve timing of an exhaust gas valve is retarded or advanced in response to a change in the phase of an exhaust gas cam shaft with respect to a crank shaft by the valve timing varying mechanism, and operation characteristics of the exhaust gas valve is switched between operation characteristics for the self ignition combustion mode and operation characteristics for the normal mode by the valve operation characteristic switching mechanism. In this way, as the operation characteristics of the exhaust gas valve is switched to the operation characteristics for the self ignition combustion mode, the exhaust gas valve is once opened and closed in an exhaust stroke, and subsequently is again opened and closed in an intake stroke. In this way, exhaust gases discharged to the exhaust passage flow back into a combustion chamber, and remains within the combustion chamber as previously burnt gases until the next combustion cycle. The previously burnt gases remaining in this manner are at higher temperatures than recirculated gases by the exhaust gas recirculating mechanism.
On the other hand, the control apparatus comprises a water temperature sensor for detecting an engine water temperature which is the temperature of cooling water of the internal combustion engine, a throttle valve opening sensor for detecting the opening of a throttle valve, an engine rotational speed sensor for detecting the engine rotational speed, and the like. This control apparatus determines whether or not the internal combustion engine is in a warm operation based on the engine water temperature, and determines operation ranges of the internal combustion engine (i.e., a load range and a rotation range) based on the opening of the throttle valve and the engine rotational speed when the internal combustion engine is in the warm operation. Then, when the operation range of the internal combustion engine is in a hot EGR range (low load and low rotational speed range) or a cold EGR range (middle load and middle rotational speed), the self ignition combustion mode is executed as a combustion mode of the internal combustion engine, and the normal combustion mode is executed when the operation range is in another range.
In this self ignition combustion mode, when the operation range of the internal combustion engine is in the hot EGR range, the valve timing varying mechanism and the valve operation characteristic switching mechanism are driven to control the amount of remaining previously burnt gases, thereby controlling the temperature of gases within a cylinder. On the other hand, when the operation range of the internal combustion engine is in the cold EGR range, the exhaust gas recirculation mechanism is driven to control the amount of recirculated gases, thereby controlling the temperature of gases within the cylinder.
According to the conventional control apparatus for an internal combustion engine described above, when the operation range of the internal combustion engine is in the hot EGR range, the valve timing varying mechanism and the valve operation characteristic switching mechanism are driven to control the amount of remaining previously burnt gases i.e., the temperature of gases within the cylinder, but the valve timing varying mechanism and the valve operation characteristic switching mechanism have response relays and lag times due to their structural characteristics, and therefore fail to appropriately control the temperature of gases within the cylinder, possibly resulting in an unstable combustion state and a lower fuel efficiency. Further, when the operation range of the internal combustion engine is in the cold EGR range, the temperature of gases in the cylinder is controlled by way of the exhaust gas recirculation mechanism, but the exhaust gas recirculation mechanism has a relatively large response delay and lag time due to its structural characteristics, and therefore suffers from a large degree to which the combustion state becomes unstable and a large degree to which the fuel efficiency is exacerbated due to a relatively large degree of reducing the control accuracy of the temperature of gases within the cylinder, and in the worst case, can experience flame off, although an auxiliary spark ignition is performed.